Voice and music mixer for use in sound recording



J. o. BAKER 2,158,268

VOICE AND MUSIC MIXER FOR USE IN SOUND RECORDING 7 May 16, 1939.

Filed April 50, 1936 (Itfomeg Patented May 16, 1939 UNITED STATES PATENTOFFICE VOICE AND MUSIC MIXER FOR USE IN SOUND RECORDING of DelawareApplication April 30, 1936, Serial No. 77,11

3 Claims.

This invention relates to the simultaneous recording of speech and musicor other acoustical effects and pertains more particularly to a methodof and apparatus for recording speech together 5 with either music orother effects in such a manner that the speech is not obscured by theaccompanying sound.

In the producing of sound records and particularly sound records toaccompany motion pictures it is customary on occasion to prepare arecord of music or sound effects and to later add other record byre-recording speech at the appropriate places. In doing this it isnecessary to have the music at a sufiiciently high level to besatisfactorily audible when there is no speech. It is, ac-

cordingly, necessary to have the speech either harsh or extremely loudor to decrease the volume of the music when speech occurs.

It is pointed out in Mueller Patent No. 1,888,467

0 that in prior practice such effects have been performed manually andthe said patent discloses the use of the special input currents tocontrol the gain of the music or effects amplifier reducing the gain ofthe amplifier when speech occurs in 25 a predetermined manner and againincreasing it at the end of the speech. Such apparatus, of course,operates with sufficient rapidity to avoid either blanketing speech bythe music or relatively silent intervals either of which may occa- 30sionally occur with manual control. As distinguished from the customarymanual method and from the method disclosed by the aforesaid Muellerpatent, I propose to control directly the sound reproducing device,which introduces the music or 35 sound effects to the recorder and toaccomplish this control from the speech amplifier. I prefer, in theperformance of my invention, to use the photoelectric type of soundreproducer and to accomplish the volume control by controlling the 40intensity of the beam of light which is directed to the film soundrecord.

One object of my invention is to provide a novel recording apparatus foradding speech to a music or effects record.

45 Another object of my invention is to provide a novel method ofre-recording sound.

Another object of my invention is to provide a photo-electric filmphonograph with automatic volume control.

50 Another object of my invention is to provide a photo-electric filmphonograph in which the volume is controlled by an independent source ofsound.

Other and ancillary objects of my invention will 55 be apparent to thoseskilled in the art from a reading of the following specification and aninspection of the accompanying drawing in which the single figure is aschematic diagram of the amplifier circuits I prefer to use and asectional diagram of the essential elements of the film 5 phonographshown in proper relation to the amplifiers.

The apparatus includes a sound recorder which is diagrammaticallyindicated at Hi. This recorder is preferably of the variable areaelectro- 10 photographic type but may be any other known type of soundrecorder capable of electrical actuation. The main recording amplifieris indicated at II. This amplifier is of a customary type includingthermionic tubes with appropriate con- 16 necting circuits and the usualappurtenances thereto. I prefer to use an amplifier embodying bothresistance and transformer coupling in order to secure any desiredfrequency characteristics but this is not essential. 20

Current is fed to the amplifier H from the mixer l2 which serves todetermine the input level to the amplifier by the potentiometer i3 andto determine the respective input levels from the film phonograph andthe speech input by the potentiometers l4 and Hi. It is not essentialthat single-resistor potentiometers, as shown, be used as these merelyschematically indicate appropriate volume control resistances which maybe simple potentiometers or potentiometric devices of T- pad or H-padtype or the equivalent. The speech input device is indicated at l6 as amicrophone. It will be apparent, however, that this may be any desiredtype of speech input or sound effect input and it may be a phonograph ofany desired type. The output from the speech input device is fed to thespeech amplifier I! which, like the amplifier ll, may be any desiredtype of thermionic amplifier and, as pointed out above, the output fromthe amplifier I! is fed through the mixer I2 and the amplifier H to therecorder ID. The music input amplifier is indicated at H! and the inputfor this is supplied by the photocell lB. The photocell I9 is suppliedwith light modulated by the film sound record 29 which in turn isilluminated by the exciter lamp 2|, the light from which is focused onthe film in the form of a fine line by the optical system 22 includingthe condenser lens 23, slit 24 and the objective In order to control theacoustic level of the music introduced I divert a portion of the outputfrom the amplifier I! through the leads 26 to the amplifier generallyindicated at 21. This amplifier includes the thermionic amplifier tube28 provided with appropriate coupling circuits. The output from theamplifier 28 is fed through a transformer 29 to the rectifier circuit 30which is a bridge circuit including four rectifiers as indicated. Itwill be apparent that this arrangement provides the rectifier circuit 30with audio frequency currents and that this rectifier changes theseaudio frequency currents into a direct current varying in accordancewith the amplitude or volume of the speech input. In other words theoutput of the rectifier provides what is generally referred to as anenvelope current varying in accordance with the input to the amplifierII.

It will be apparent that for the purpose of this inventionit isnecessary to decrease the output from the amplifier l8 in accordancewith the increase of output from the rectifier 30. In order to do this Iprovide a shutter 3| which is movable about the pivot 32 by the actionof the magnet 33. This shutter is located between the filament 34 of theexciter lamp 2| and the slit member 24. As indicated in the drawing thefilament 34 is preferably of the coil type which has a finite diameter.When the output from the rectifier 30 to the magnet 33 increases, themagnet draws the member 35 downward against the action of the spring 36,thereby raising the shutter 3|. As the shutter 3| rises it masks more orless of the Width of the coil filament 34 from the slit 24, therebycausing the slit 24 to pass from full illumination into the graduallyincreasing shadow of the shutter 3| which is referred to as the penumbraand at maximum excitation of the magnet 33 and corresponding maximumelevation of the shutter 3| to approach the total darkness which isreferred to as the umbra. It will be apparent that by properly locatingthe shutter and magnet in relation to the filament 34 I may adjust thedevice to provide any desired degree of maximum or minimum shade orboth; and that I may adjust the rate of change of shade andcorrespondingly the rate of change of music input in any ratio to thespeech input that I- desire by adjusting the sensitivity of theamplifier 2'|,-this change of sensitivity may be accomplished in anydesired manner although the most convenient way is to use a variable mutube at 28 and to adjust the grid bias thereon by varying the value ofthe resistor 31 or by using battery bias instead of the biasing resistor31 and varying the value thereof.

Having now described my invention, I claim:

1. A film phonograph comprising a light source, an optical system fordirecting light from said source upon a film sound record, photoelectricmeans in cooperative relation to the said optical system, a volumecontrol comprising an electrically actuated shutter between said lightsource and said optical system, and amplifying means and rectifyingmeans controlling said shutter inversely in accordance with sound fromanother source.

2. Apparatus of the class described comprising sound reproducing means,amplifying means, mixing means and recording means connected insequence, a second sound reproducing means and amplifying meansconnected through said mixing means to said recording means, and meansconnecting the second amplifying means with a first sound reproducingmeans for controlling the volume of sound produced thereby, whereby thevolume of sound recorded from said first sound reproducing means may bevaried while maintaining the amplification ratio of said first amplifierconstant.

3. Record re-recording apparatus including a photoelectric filmphonograph, including means for directing a beam of light through asound record to a photoelectric cell, a second source of electricalimpulses corresponding to sound waves, and means for controlling theintensity of said beam of light in accordance with the amplitude of thesounds from the second source.

JUDD O. BAKER.

